在超类方法中使用子类成员变量？

Question

I have a base class and subclass. Base class has common methods and its implementation which I want to use in subclass but I want to use subclass member variable instead of superclass. I do not want to rewrite the same method in subclass. Is there a way in Java to achieve this.

Answer 1

You can use a method to access the member and override it in subclasses.

Class A{
  public void DoStuff(){
     int aux = getResource; 
     /*cool things with aux*/
  }
  protected int getResource(){
    return internal_member;
  }
  private int internal_member;
}

Class B extends A{
  private int another_member;
  @Override
  public int getResource(){
     return another_member;
  }

}

But take into account that this will not prevent people chaging class A from using the member directly, It might be better to create a base class for the members and the getters.

Another Option, as some people outlined before is to have the data member in the base class as protected and initialize it in the subclass:

Class A{
  public void DoStuff(){
     /*cool things with internal_member*/
  }
  protected List internal_member;
  A(){internal_member = /*Set here a value*/}
}

Class B extends A{
  B(){internal_member = /*Set a different value here! you can even declare a member and assign it here*/}

}

You can use constructors with arguments if you need.

Answer 2

You could create a protected setter on the member variable & then override the value of the super's variable within the constructor of the subclass:

class Animal {
   private String voice = "Oooo";

   protected void setVoice(String voice) {
       this.voice = voice;
   }

   public void speak() {
       System.out.println(this.voice);
   }

}

class Dog extends Animal {

    public Dog() {
        setVoice("woof"); 
    }

}